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Q&A: General Astronomy and Space Science
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Q:
Every picture of a spiral galaxy including our own, depicts a
very bright, spherical center ... I assume a dense cluster of
stars. We can see this bright center in distant galaxies, and
I've always wondered, why we don't see the bright center of our
own. Or, do we, and I don't know what I'm looking at? It seems
it would be far brighter than our Sun, even though we are at the
far edge of the galaxy. Thanks for helping me find it!!
A:
There is a spherical region surrounding the central region of
our galaxy known as the "bulge" which is indeed dense with
stars. It is actually more luminious than it appears because its
light is diminished by absorption from dust as well as distance
by the time it reaches us. The Earth is situated in the middle
of the plane of our galaxy where the absorption towards the
center is maximum. The surface brightness, or brightness per
angular area, of the bulge is much less than the Sun's because
of this absorption and the fact that the stars, though dense,
still fill only a small fraction of the volume.
The galaxies that appear in the astronomy books are selected
because they are the most photogenic and are generally not
typical. We look at them face on which is a viewing direction
where there is little absorption.
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